In the Atlantic City specimen the superior lateral free margin of the symphysis is straight, while in the type it is much elevated. This is no doubt due to difference in age and possibly in sex. The type shows three or four mental foramina, while the Atlantic City specimen has one large posterior one and seven smaller ones anterior to it.
Another peculiarity of the latter specimen is that the coronoid process is situated much in advance of the condyle, while the angle extends considerably behind it. In the type both are nearly in line with the condyle. I am unable to explain this difference.
In the Atlantic City specimen the axis of the tooth where it emerges from the alveolus is 91 mm. from the end of the jaw. The portion of the tooth above the alveolus is 11 mm. long at the base and 12 mm. high. It is conical and sharp pointed, and is inclined forward and a little outward, especially at the tip. At the alveolus the transverse breadth of the tooth is 5 mm. The much larger tooth in the type indicates that that specimen was a male.
The mandible of the Atlantic City specimen of M. europæus differs from that of M. bidens in the relative shortness of the symphysis, the large number of mental foramina, the more anterior position of the tooth, and the direction of the crown, which is forward instead of backward.
Dimensions of the type and two other skulls of Mesoplodon europæus.
Column headings: A: English Channel, type,a adult. B: North Long Branch, New Jersey, female, adult. C: Atlantic City, New Jersey, 23346 U.S.N.M., male, young.
| Measurements. | A | B | C |
|---|---|---|---|
| mm. | mm. | mm. | |
| Total length | 762 | (b) | 675 |
| Length of rostrum | 459 | ... | 427 |
| Tip of beak to posterior end of pterygoids | 561 | ... | 525 |
| Height from vertex to end of pterygoids | c292? | 283 | 256 |
| Breadth between orbits | 327 | d325 | d287 |
| Breadth between zygomatic processes | 360 | e325 | 302 |
| Breadth at anteorbital notches | 210 | 205 | f182 |
| Breadth of beak at middle | 66 | ... | 60 |
| Depth of beak at middle | 54 | ... | 40 |
| Greatest breadth of premaxillæ proximally | 168 | 147 | 142 |
| The same, in front of anterior nares | 111 | 99 | 104 |
| Breadth of anterior nares | 51 | 45 | 42 |
| Length of temporal fossæ | 102 | 115 | 101 |
| Breadth between temporal fossæ | 228 | 212 | 208 |
| Breadth of foramen magnum | 42 | 34 | 34 |
| Length of mandible | 654 | ... | 565 |
| Length of symphysis | 135 | ... | 116 |
| Greatest depth of mandible | 120 | ... | 101 |
a Dimensions taken from Van Beneden and Gervais’ figures. b Beak lacking. Length from occipital condyles to base of beak (straight), 312 mm. c Pterygoids broken. d At middle. e Estimated. One zygoma is broken. f Least.
VERTEBRÆ.
The vertebral formula of three specimens of M. bidens and of the Atlantic City specimen of M. europæus is as follows: